An optical transport network (OTN) is a transport network based on a wavelength-division multiplexing technology and networking at an optical layer, and is a mainstream transport network technology at present. Due to explosive increase of Internet Protocol (IP, Internet Protocol) services transported on a network and other data services based on packet transport, requirements on a transmission capacity increase rapidly and continuously. With maturity and application of a dense wavelength division multiplexing (DWDM, Dense Wavelength Division Multiplexing) technology and an optical amplifier (OA, Optical Amplifier) technology, a transport network is evolving into an optical transport network based on an optical networking technology. The emergence of a transport network based on the OTN gradually turns an intelligent optical network expected by people into reality and provides network operators and customers with a secure, reliable, cost-effective, customer-irrelevant, manageable, operable, and efficient new-generation optical transport platform. On the OTN, service data is first encapsulated into an optical payload unit (OPU, Optical Payload Unit) by using a certain encapsulation method, then mapped to an optical channel data unit (ODU, Optical channel Data Unit), and then mapped to an optical transport unit (OTU, Optical Transport Unit). After electrical-optical conversion, a network hierarchy of the optical layer sequentially includes an optical channel layer, an optical multiplexing section layer, and an optical transport section layer. According to rates of the ODU, the ODU is mainly classified into types shown in table 1.
TABLE 1SignalData rate (unit: Gigabit per second)ODU01.24416ODU12.49877512605042ODU210.0372739240506ODU2e10.3995253164557ODU340.3192189830509ODU3e241.7859685595012ODU4104.794445814978
On the OTN, a lower order ODU can be multiplexed into a higher order ODU. For example, when an ODU1 is compared with an ODU2, the ODU1 is a lower order ODU, and the ODU2 is a higher order ODU; and when the ODU2 is compared with an ODU3, the ODU2 is a lower order ODU, and the ODU3 is a higher order ODU. Therefore, before the ODU is mapped to the OTU in the foregoing description, it is possible that this ODU needs to be multiplexed as a lower order ODU into a higher order ODU.
An important feature of the OTN is that the OTN not only provides cross-connection and multiplexing (which can be performed by using a reconfigurable optical add-drop multiplexer (ROADM, Reconfigurable optical add-drop multiplexer) at present) of a wavelength-level optical channel, but also provides cross-connection and multiplexing at a sub-wavelength granularity ODU level.
Both the cross-connection and the multiplexing of the ODU are performed at an electrical layer by electrical signal processing. That is, to perform the cross-connection of the ODU, first, an optical signal needs to be converted into an electrical signal by using an optical receiver, and then the ODU is extracted from the electrical signal layer by layer; then electrical cross-connection is performed, then encapsulation is performed layer by layer, and then conversion to an optical signal is performed by using an optical transmitter. Evidently, an intermediate node of the OTN needs to perform optical-electrical-optical conversion on transmitted data and a great deal of electrical signal processing, a data processing process is complex, and a data processing delay is relatively great.